Brucella found in Kenya’s rapidly growing pig sector

James Akoko is an Afrique One-ASPIRE Fellow, who is undertaking a PhD program at Maseno University in Kenya. Afrique One-ASPIRE (Afrique One-African Science Partnership for Intervention Research Excellence (ASPIRE)) is one of the 11 Developing Excellence, Leadership, and Training in Science in Africa (DELTAS Africa) programmes. DELTAS Africa funds collaborative consortia led by Africa-based scientists to amplify Africa-led development of world-class research and scientific leaders on the continent, while strengthening African institutions. DELTAS Africa is implemented through the AESA Platform. AESA (Alliance for Accelerating Excellence in Science in Africa) is a funding, agenda-setting, programme management initiative of the African Academy of Sciences (AAS), the African Union Development Agency (AUDA-NEPAD), founding and funding global partners, and through a resolution of the summit of African Union Heads of Governments. DELTAS Africa is supported by Wellcome and the United Kingdom Foreign, Commonwealth and Development Office (FCDO formerly DFID).

Summary

Brucellosis is a neglected zoonotic disease that is usually found in cattle, sheep and goats. This study is the first to detect and report Brucella infection in pigs in Africa using molecular techniques. This has major consequences for Brucellosis control and food safety management and emphasizes that pigs should be included in brucellosis control programs in Kenya, which have mostly targeted ruminants.         

Background

Brucellosis is a neglected zoonotic disease with worldwide distribution. It affects a broad range of wild and domesticated animals and is responsible for economic losses from reduced milk yields, infertility and abortions in infected animals. While there are numerous species of the bacterial genus Brucella, those commonly associated with human infections are B. melitensis, B. abortus and B. suis, largely affecting small ruminants, cattle and pigs, respectively.  Humans can contract brucellosis via direct or indirect contact with infected animals and through the consumption of under-cooked or raw animal products; over 500,000 annual new cases are reported worldwide. Brucellosis in humans causes high fever, body pain, weakness, abdominal pain and weight loss. In Kenya, brucellosis is classified among the top priority zoonotic diseases for integrated ‘One Health’ control, but the focus is limited to ruminants, which have so far been identified as the main source of human infection of Brucella.

One of the three most common pig zoonotic pathogenic species transmitted to humans is B. suis. Nonetheless, knowledge of pig brucellosis in Kenya remains sparse: the only documented information on the disease was produced more than four decades ago. Presently, pork production and consumption are among the most rapidly growing livestock sectors in Kenya, with a forecast overall production growth rate of over 200% for the period 2000-2030. Fortunately, molecular-based assays for the rapid and specific detection of Brucella DNA has also significantly advanced. Yet, the understanding of the role of pigs in the transmission dynamics of brucellosis remains limited. Previous studies have investigated pork value chains and their potential role in the transmission of other priority zoonoses.

Description of the study

Our study was conducted to detect and identify Brucella spp. in pigs entering the Nairobi pork market to assess product safety. In doing so, we identified significant differences from our current understanding of host species distribution and diagnostic challenges for brucellosis in pigs. A total of 700 blood samples were collected from pigs presented for slaughter in a fresh pork slaughterhouse in Nairobi. The samples were then screened in parallel, using both standard Rose Bengal Test (RBT) and a commercial-based competitive Enzyme-Linked Immuno-sorbent Assay (cELISA) to detect the presence of antibodies against the bacterium (Brucella). All sera positive by RBT and 16 randomly selected negative samples were further tested using two molecular biology methods (standard PCR and Real-Time PCR) that detect the presence of the bacterial DNA.

Study outcome

Pigs investigated originated from all the six pig producing regions in Kenya. A prevalence of 0.57% (n = 4/700) was estimated using RBT; although this is low, it is almost three times higher than the prevalence reported in 1978. None of these samples were positive on cELISA. All RBT positive sera were also positive by both PCRs, while two sero-negative samples also tested positive on Real-Time-PCR (n = 6/20). Brucella abortus was detected in four out of the six PCR positive samples through a real-time multiplex PCR.

Lessons learned

Most studies in Kenya have reported the presence of Brucella antibodies or infections in cattle, sheep and goats. But this study shows that pigs are also exposed to Brucella infection. This has major consequences for Brucellosis control and food safety management.

While pigs are traditionally known to be infected by B. suis, our study detected B. abortus, a pathogen that has always been found in ruminants. Close interaction between pigs and cattle in farm settings may have facilitated cross-transmission of B. abortus to pigs.

Most countries in Africa target ruminants (cattle, sheep and goats) in brucellosis control programs. The detection of zoonotic spp. of Brucella in pigs suggests the possibility that pigs may also be a risk factor of brucellosis transmission to farmers, slaughterhouse workers and those consuming raw or undercooked pork, and should therefore be included in brucellosis control programs.

^{Picture: Free ranging pigs in a peri-urban area in Kenya}

Study impact

This study confirms the presence of Brucella spp. in pigs. This calls for further investigation of the epidemiology and role of pigs in the transmission of brucellosis, given the limited data available. We have demonstrated that B. abortus, which has been associated mostly with infection in cattle, can also infect pigs. Results show that cross-transmission of Brucella spp. from one species of livestock host to another is possible, especially in areas with close contact among different animal species. The study has also shown that pigs may play a role in transmitting brucellosis to unsuspecting human populations, given the detection of zoonotic spp. of Brucella (B. abortus) in pigs. Therefore, policy should mandate the inclusion of pigs in brucellosis control programs, for effective control of the disease in Africa, especially in areas with close contact among different animal species. Both serological and molecular techniques can be used to detect the presence of antibodies and Brucella DNA, respectively.

Full publication details can be found at: https://doi.org/10.1186/s12917-020-02346-y